1. Field of the Invention
The field of the invention disclosed herein is directed to phase shift detection for use in laser radar ranging systems.
2. Description of Related Prior Art
Continuous-wave (CW) radar is a type of radar in which the transmitter output is uninterrupted, as compared to phase radar which consists of short pulses. One of the advantages of CW radar is its ability to measure velocity with extreme accuracy by means of the Doppler shift in the frequency of the echo. In order to measure the range of a target a waveform must be generated by "modulating" or "beating" the continuous wave output into a waveform from which a shift can be measured.
In the prior art, waveform generation has been accomplished with use of Amplitude Modulation (AM), Frequency Modulation (FM), or pulsing schemes for use in microwave and laser radar systems.
AM and FM radar range systems of CW radar utilizes a carrier frequency or carrier amplitude of the transmitted signal which is varied at a uniform rate to produce a waveform. Range is determined by comparing the frequency of the echo with that of the transmitter. An AM system is simple but very inefficient with ambiguity intervals present. The FM system solves the ambiguity intervals yet is very expensive and complicated.
A pulse radar range system is a modified form of either the AM or FM system which employs long or short, but not continuous transmission. This type of system is easy to process and solves the ambiguity interval, but is extremely inefficient and very expensive.
The laser radar range system was developed to overcome the inefficient characteristics of the other systems while taking advantage of the extreme precision inherent to a laser. The laser acts as a carrier wave, but still must be modulated with another type of method to generate a waveform. While this system is extremely precise, there still are problems inherent to this system due to the modulation method used.
There has been a need in the art for a laser radar range system which utilizes inexpensive components and generates an waveform which is efficient without ambiguity intervals within the desired image.
The primary objective of this invention is to provide a method for generating a multiple frequency shifted waveform for use in laser radar ranging systems which is efficient in delivering maximum power available to a target. A secondary objective of this invention is to provide an apparatus for generating a multiple frequency shifts/waveforms in laser radar ranging systems that uses simple inexpensive components.